Reversible electrical percolation in a stretchable and self-healable silver-gradient nanocomposite bilayer

The reversibly stable formation and rupture processes of electrical percolative pathways in organic and inorganic insulating materials are essential prerequisites for operating non-volatile resistive memory devices. However, such resistive switching has not yet been reported for dynamically cross-linked polymers capable of intrinsic stretchability and self-healing. This is attributable to the uncontrollable interplay between the conducting filler and the polymer. Herein, we present the development of the self-healing, stretchable, and reconfigurable resistive random-access memory. The device was fabricated via the self-assembly of a silver-gradient nanocomposite bilayer which is capable of easily forming the metal-insulator-metal structure. To realize stable resistive switching in dynamic molecular networks, our device features the following properties: i) self-reconstruction of nanoscale conducting fillers in dynamic hydrogen bonding for self-healing and reconfiguration and ii) stronger interaction among the conducting fillers than with polymers for the formation of robust percolation paths. Based on these unique features, we successfully demonstrated stable data storage of cardiac signals, damage-reliable memory triggering system using a triboelectric energy-harvesting device, and touch sensing via pressure-induced resistive switching.

. These results fully support our materials strategy on intrinsically stretchable RRAM for realizing the strain-insensitive stable memory.

Supplementary Fig. S18 | Current-voltage switching behavior of SS-RRAM before/after
self-healing process. The black-colored and blue-colored curves correspond to I-V data before and after the healing process, respectively.

Supplementary Note #3
To confirm the electrical property of the memory array, we performed the I-V switching test of the memory array before and after conversion. In the resistivity switching test of 1 × 4 array, the farthest end of the word line was probed from the bit line of any testing cell. So that the electrical test possibly included the interference of non-selected memory cells. Each I-V curve of 1 × 4 array was shown in Fig. 4h, in which the electrical behavior was likely to be the same with the 1 × 1 memory cell in Fig. 2b, this result indicated that the resistivity-switching of cells in the 1 × 4 array was also operating well. Next, the measured 1 × 4 array was converted into a 2 × 2 array. After the healing process, I-V switching test of each cell was performed in a rearranged 2 × 2 array as shown in Fig. 4i, Testing lines of each cell were intentionally selected to pass through the healed bit line, so that it confirmed the full operation of 2 × 2 array. The resistivity-switching for each cell remained in the same range of the Set and Reset bias of 1 × 1 memory in Fig. 4b. Figure 4j presented the resistance state of cells in 2 × 2 and 1 × 4 arrays.
The resistance of each test was measured with reading one-fifth of set and reset bias. Even though the resistance of HRS and LRS had a certain distribution for each cell, all memory cells still exhibited the resistance window higher than ~10 5 . The corresponding I-V curve. c, Retention data of the SS-RRAM before and after applying a water drop. As a simple model, the V (voltage)-Q (charge)-x (distance) relationship can be used to interpret the dependence between the output and contact height in a TENG system. The size of the area covered by the metal was assumed to be larger than their separation distance, and the induced tribo-charges were uniformly distributed at the surface with insignificant decay. With the above assumption, the electric field equation can be represented using the parallel plate model and Gaussian theorem. In the conductor-to-dielectric system, the electrostatic field between the top and bottom electrodes was expressed in two parts, namely Eair (air gap) and Edielectric (dielectric), given by:

Supplementary
(1) air gap: where , , 0 , ( ), and are the amount of charge transferred between two electrodes, the size of the metal, permittivity of air, surface tribo-charge density, and permittivity of the dielectric, respectively. The potential difference between the two electrodes can be expressed as follows: ( Voltage drop at a SS-RRAM depends on mechanical moving distance of a TENG. When enough power was delivered to the RRAM HRS switched to LRS. Thus, only a minor voltage drop was observed after the switching. c, In-situ voltage drop at the SS-RRAM in a self-powered system.

Supplementary Note #5.
Prior to the integration of all components, a TENG was tested depending on pushing height at 100 GΩ and thus proper condition of power outputs could be selected for triggering RRAM. The output voltage of TENG increased as the deviation of pushing height increased. Each height was tested 20 cycles. Afterward the RRAM in HRS was connected to a circuit, the triggering voltage was found to be ~2 V, which was mostly identical value with the former I-V test shown in Figure   2g. Once the HRS of RRAM changes to LRS during the operation of TENG voltage crossed